Apparatus for damping the pressure increase of hydrostatic drives

ABSTRACT

An apparatus for damping the pressure increase of hydrostatic drives, especially axial piston pumps, with swash plate control and pre-biased oil circulation, wherein the pressurized oil compartment of an adjustment cylinder is connected with the lower pressure side of the oil infeed of the pump via a check or nonreturn valve which opens in the direction of the low pressure conduit of the oil infeed.

United States Patent [191 Schlecht Dec. 17, 1974 APPARATUS FOR DAMPINGTHE [56] References Cited PRESSURE INCREASE OF HYDROSTATIC UNITED STATESPATENTS DRIVES 3,543,508 12/1970 Schwab 60/445 [75] Inventor: KarlSchlecht, Bernhausen Stuttgart, 31650408 3/1972 Isaac.

Germany 3,660,975 5/1972 Martm et al. 60/444 [73] Assignee: Pulzmeisterlnterholding GmbH, P i y Examinr-Wil]iam L.,Freeh Zurich, SWitZerlandAssistant Examiner-Gregory Paul LaPointe [22] Filed: 20, 1973 Attorney,Agent, or Firm-Werner W. Kleer nan [21] Appl. No.: 333,652 [57] ABSTRACTAn apparatus for damping the pressure increase of by [30] ForeignApplication priority Data 'drostatic drives, especially axial pistonpumps, with Feb [972 Germany 1 2208172 swash plate control andpre-biased oil circulation,

' wherein the pressurized oilcompartment of an adjust- [52] us Cl417/212 60/444 417/254 ment cylinder is connected with the lowerpressure' [51] Int Cl F04 4 F15b 15/18 side of the oil infeed of thepump via a check or non- [58] Field 415555 417/212 2i 3 218 222 returnValve which opens in the direction of the pressure conduit of the oilinfeed.

4 Claims, 2 Drawing Figures PATENTEL 5551 7 4 snmlnrg Fig.

APPARATUS FOR DAMPING THE PRESSURE INCREASE OF HYDROSTATIC DRIVESBACKGROUND OF THE INVENTION The present invention relates to a new andimproved construction of apparatus for damping the pressure increase ofhydrostatic drives wherein a controllable axial piston pump, preferablyequipped with a swash or wobble plate, drives a motor or selectively thehydraulic cylinder of a concrete pump.

With such type drives oftentimes there occur rapid load changes at themotor, even if such operates at a constant rotational speed. In the caseof concrete pumps operating according to'a rotor principle or pistondisplacement principle, such'is the case if, after each stroke change orafter each operable activity of a displacement roller, the concretecolumn, which is at rest during the stroke change in the conveying line,again must be accelerated. The rotational movement of the oil motor orthe speed of the piston rods of the conveying cylinder is always auniform one because it is acted upon by a displacement pump.

The large forces required for the renewed accelera tion of the concretecolumn leads to a brief high pressure increase at the high pressure sideof the drive. The pressure peaks are so high that the overpressure valveresponds and there is perceivable a certain development of heat. On theother hand, the sudden accelerated concrete column produces undesirablereaction forces which, for instance, can result in the concrete line orconduit being exposed to impacts.

In order to overcome these drawbacks it would be conceivably possible,after each stroke reversal or change, to rock the hydraulic pump intoits null conveying position and to allowsuch tobe slowly controlled inorder to realize a slow feed of the concrete column. Yet in practicethis is not possible for a number of reasons, particularly also becausethe time span between the point in time of reversing the control of theconveying pistons and themoment at which such impinge against theconcrete columns and begin to accelerate such occur quite differently,depending upon the composition of the concrete and the operating speedof the pump.

To avoidsuch acceleration peaks which oftentimes exceed 200 percent ofthe conveying pressure, it is equally not possible to employ the knownpressure compensation. During conveying of the concrete the pressurelevel continuously changes because the consistency of the concrete andthe length of the conveying conduit or lines varies.

SUMMARY OF THE INVENTION Hence, it will be recognized that thisparticular field of technology is still in need of apparatus for dampingthe pressure increase at hydrostatic drives in a manner whicheffectively and reliably overcomes the aforementioned drawbacks existingin the state-of-the-art constructions. It is therefore a primary objectof the present invention to provide an apparatus which effectively andreliably fulfills the needs existing in the art and overcomes theaforementioned drawbacks present with the prior art constructions.

Another and more specific object of the present invention aims atlimiting the speed of increase of the pressure whenever the pressureincrease occurs and irrespective of its magnitude, and specificallyparticularly during constant rotational speed of the pump or the oilmotor or during uniform speed of the conveying cylinder.

Now in order to implement these objects and others which will becomemore readily apparent as the description proceeds, the inventionproposes a novel solution while resorting to the use of a phenomenonwhich previously was considered to be disadvantageous. In most of thehydrostatic pumps, especially however axial piston pumps with swash orwobble plate control, during the pressure increase there occurs anincreased escape of leakage oil. This can be essentiallyexplained interms of the variable gap widths under which the control plates of suchpumps move towards one another with and without pressure. With a closedcirculatory flow, this leads to the result that with a sudden pressureincrease the conveyed quantity'of the supply pump is often notsufficient. As a result, the pre-bias of the oil collapses at the lowpressure side, leading to annoying and damaging cavitation effects. Assoon as the maximum pressure has been reached, the escape of leakage oilagain assumes normal values.

Since most of the hydraulic pumps in modern drives are no longermechanically controlled as concerns their conveying length, ratherthrough the agency of hydraulic adjustment cylinders, for instance as afunction of the rotational speed of the drive motor, the inventionproposes that with a hydraulic pump, preferably an axial piston pumphaving a swash or wobble plate control, and which pump is equipped witha hydraulic adjustment cylinder and at the pre-biased oil circulationsystem with a supply pump and the therewith associated conventionalfilling pressure limiting devices, flu-- shing' and reversing valves,the pressurized oil com partment of the adjustment cylinder is connectedwith the low pressure side oil circulation system of the pump via acheck valve. When there is a pressure drop at the low pressure sideowing to an increased leakage oil consumption, pressurized oil flows outof the control cylinder through the check valve to the low pressure sideof the pump and this check valve then prevents flow of the oil in theopposite direction. Consequently, there is thus temporarilyprevented'rocking or swiveling of the pump and therefore the pressureincrease velocity at the pressure line.

With the apparatusof the'type proposed by the invention, wherein theconveyed quantity is controlled independently-of the conveying pressureby means, of internal servo-adjustment of the swash or wobble plate, theservo-control advantageously embodies an external adjustment leverhinged with the outer adjustment cylinder, and the inner adjustmentcylinder likewise possesses a connection with the low pressure line inwhich the check valve is arranged. The outer adjustment cylinderadvantageously possesses a spring, the restoring force of whichcorresponds to a pressure which is only slightly less than the pressureprevailing at the low pressure line of the pump. Both the outeradjustment'cylinder as well as also the low pressure line connected withsuch cylinder via the check valve as well as also the ser vo-valve aresupplied by an external auxiliary pump.

An advantageous further embodiment of the apparatus consists in thefeatures that the servo-valve is coupled via a check valve with theauxiliary pump. The supply pump which is usually flanged to the pump canthen be dispensed with for this type of modified equipment. 1

A further variant construction of the apparatus of this developmentcontemplates that when dispensing with the use of an auxiliary pump anda throttle arranged after such auxiliary pump, the adjustment cylinderis connected'with a mechanical adjustment mechanism and the side at thefloor or bottom of the adjustment cylinder is connected via a regulatingthrottle and I a check valve with the servo-control pressure side of thepump.

BRIEF DESCRIPTION OF THE DRAWINGS description thereof. Such descriptionmakes reference to the annexed drawings wherein: Y

FIG. 1 illustrates an exemplary embodiment of apparatus possessing aninternal servo-adjustment of the swash or wobble plate of an axialpiston pump andan auxiliary pump; and

. FIG. 2 is a modified form of the apparatus depicted in FIG. 1 withoutan auxiliary pump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now thedrawings, it is to beunderstood that at the momentary low pressure side1a of the main circulation system 50 of the pump 1 oil is conveyedfrom-a supply pump 5, which is protected by a filling pressure-safetyvalve 6, through the agency of a check valve ornonretum valve 7. For thesake of simplicity in illustration, the circulation system has only beendepicted for a non-reversible pump which conveys in one direction. Thesupply pump 5 also conveys oil to a servo-valve mechanism by means ofwhich the piston 8a of an inner or internal adjustment cylinder 8 can beoutwardly displaced or ejected. The piston rod 8b thereof is connectedvia a rigid mechanical connection 9 with an adjustment element,schematically indicated at 9a, of a conventional and therefore notparticularly illustrated swash plate of the pump 1. Between the pistonrod 8b of the adjustment cylinder 8 and the servo valve mechanism 10there is provided a mechanical return device 20. As soon as a shaft 4drives the pump 1 then this pump, by means of a servo-adjustment, isswitched to the desired delivery capacity when the adjustment lever 12of the servo-valve mechanism 10 is rocked out of its null position. Thisoccurs under the action of the external or outer hydraulic adjustmentcylinder 13, the piston 13a of which is retained in its null positionthrough the agency of a return spring 17. In the embodiment underconsideration the required adjustment pressure is generated by anauxiliary pump 14 which, as a general rule, is driven by the same motoras the pump 1 and therefore has a rotational speed proportional to thepump 1 and conveys in the direction of a regulation throttle 15.

With a certain adjustment of the throttle 15 the control oil pressurewhich is effective in the adjustment cylinder 13 increasesproportionally as a function of the rotational speed of the drive motor.At a certain rotational speed the pre-bias force of the spring 17 isovercome, the piston 13a of the adjustment cylinder 13 is displacedwithin the compartment 13b of the adjustment cylinder 13, and therefore,the pump 1 is switched over into its delivery or conveying mode via theservo mechanism 10 which is acted upon by the adjustment lever 12. Theauxiliary pump 14 generates a maximum oil pressure which, limited by thethrottle 15 and, if desired, a further overpressure valve, preferably isat a value slightly below the low pressure prevailing in the conduit orline 3.

Now if with a constant rotational speed there occurs an operatingcondition for the main pump 1 which results in a rapid rather pronouncedpressure increase at the high pressure conduit or line 2, then there isan increased leakage oil escape out of the closed working circuit intothe pump housing which is vented to the tank and which with normaldimensioning of the supply pump 5 can no longer be made up by thelatter. As a result, there is present a pressure drop at the lowpressure line 3 and therefore the danger that cavitation effects occur.However, suchis prevented by the check valve 16 through which thepressurized oil flows into the low pressure line 3 from theauxiliarypump 14 or the control chamber of the adjustment cylinder 13. With anauxiliary pump 14 which is designed as concerns its delivery capacity tothe corresponding operat ing conditions, the return spring 17accordingly can displace the piston 13a through a greater or lesserextent into the adjustment: cylinder 13. As a result the conveyedquantity of the main pump 1 is temporarily reduced via the adjustmentlever 12 anad the servomechanism 10 and specifically for such length oftime as there exists the increased consumption of leakage oil due to theincrease in pressure and which exceeds the delivery capacity of thesupply pump 5 and the auxiliary pump 14.

Due to this cooperative action there is not only made-up the increasedleakage oil consumption of the pump but at the same time owing to thereduction of the angle of attack of the wobble plate the pressureincrease is limited by the reduced delivered capacity or conveyedquantity. The-speed of the pressure increase can be controlled in asimple manner in that the delivered capacities of the supply pump 5 andthe auxiliary pump l4are coordinated to one another. For instance,

the supply pump 5 can possess a constant delivery capacity starting froma certain rotational speed; the main pump then operates at .highrotational speeds and higher pressure loads in an increasing softermanner with respect to the pressure increase.

With a pressure drop in the low pressure conduit or line 3 there is notonly infed thereto oil from the outer adjustment cylinder 13 but alsofrom the inner adjustment cylinder 8 via the check valve 18.

Now with the modified version of equipment as de-' picted in FIG. 2, andwherein here no auxiliary pump is provided, the housing of theadjustment cylinder 13 ,is rigidly connected with a mechanicaladjustment mechanism. The adjustment cylinder 13 serves as anintermediate element in the mechanicaladjustment. The floor or bottomside of the adjustment cylinder 13 is continuously connected via aregulation or control throttle 52 and a check valve 1 l with theservo-control pressure side of the supply pump 5.

If the pump is mechanically switched into its conveying or delivery modeand if during operation thereof there occurs a sudden increase inpressure, then, the piston 13a of the adjustment cylinder 13 cantemporan ily discharage fluid via the check valve 16 into the lowpressure conduit or line 3. The compartment 13b of the adjustmentcylinder 13 is less rapidly charged by the supply pump 5. As a result,there is a temporary pivoting back of the adjustment lever 12, that isto say, a decrease in the delivery or conveying capacity of the pump 1with subsequent repositioning of the adjustment lever after the pressureincrease in the main conduit or line 2 has slowly been completed.

The speed of the pressure increase is limited in known manner for allservo-controlled pumps by an inflow throttle arranged forwardly of theservo-slide valve mechanism 10, which can also be designed to becontrollable. An apparatus of the described type can also be separatelyinstalled in a very simple manner as a supplementary unit at drives ofthis type which are already in operation.

While there is shown and described present preferred embodiments of theinvention, it is to be distinctly understood that the invention is notlimited thereto, but may be otherwise variously embodied and practicedwithin the scope of the following claims. ACCORD- INGLY,

What is claimed is:

1. An apparatus for damping the pressure increase of hydrostatic drives,especially axial piston pumps with swash plate control and pre-biasedoil circulation system, the improvement comprising an adjustmentcylinder having a pressurized oil compartment, a pump, an oil infeedmeans including an oil infeed line for the pump, a check valve, thepressurized oil compartment 2. The apparatus as defined in claim 1,wherein the external adjustment cylinder is equipped with a spring,

the restoring force of which corresponds to a pressure which is onlyslightly less than the pressure prevailing at the low pressure infeedline of the pump.

3. The apparatus as defined in claim 2, further including an externalauxiliary pump for supplying both the external adjustment as well asalso via the check valve the low pressure infeed line and theservoadjustment means.

4. The apparatus as defined in claim 1, further including a check valvemeans for connecting the servoadjustment means with the auxiliary pump.

1. An apparatus for damping the pressure increase of hydrostatic drives,especially axial piston pumps with swash plate control and pre-biasedoil circulation system, the improvement comprising an adjustmentcylinder having a pressurized oil compartment, a pump, an oil infeedmeans including an oil infeed line for the pump, a check valve, thepressurized oil compartment of the adjustment cylinder being flowconnected with the low pressure side of the oil infeed line of the pumpvia the check valve, said check valve opening in the direction of thelow pressurE infeed line, an internal hydraulic servo-adjustment means,said adjustment cylinder defining an external adjustment cylinder, aninternal adjustment cylinder, said servo-adjustment means incorporatingan external adjustment lever hingedly connected with the externaladjustment cylinder, and a further check valve for flow connecting theinternal adjustment cylinder with the low pressure infeed line.
 2. Theapparatus as defined in claim 1, wherein the external adjustmentcylinder is equipped with a spring, the restoring force of whichcorresponds to a pressure which is only slightly less than the pressureprevailing at the low pressure infeed line of the pump.
 3. The apparatusas defined in claim 2, further including an external auxiliary pump forsupplying both the external adjustment as well as also via the checkvalve the low pressure infeed line and the servo-adjustment means. 4.The apparatus as defined in claim 1, further including a check valvemeans for connecting the servo-adjustment means with the auxiliary pump.